1. Field of the Invention
The present invention relates to a method of attaching a nozzle plate to an actuator for an ink jet print head. More particularly, the present invention relates to a method of attaching the nozzle plate to the actuator through thermally hardening adhesive provided between the nozzle plate and the actuator.
2. Description of Related Art
In order to produce an ink jet print head, an actuator and a nozzle plate are first produced. The actuator is formed with a plurality of ink channels. The ink channels are arranged with a uniform interval. The nozzle plate is formed with a plurality of nozzles. The number of the nozzles on the nozzle plate is the same as that of the ink channels. The nozzles are formed to be arranged with an interval equal to that of the ink channels. The intervals are measured under a room temperature when the channels and the nozzles are produced.
The nozzle plate is then attached onto the actuator in a manner described below with reference to FIG. 1.
First, the nozzle plate 4 is placed on the actuator 2 with epoxy resin provided therebetween so that each nozzle is precisely located on a corresponding ink channel.
Then, the nozzle plate 4 and the actuator 2 are mounted in a jig 50 shown in FIG. 1. In the jig 50, the nozzle plate 4 and the actuator 2 are sandwiched between a holding plate 41 and a base block 42. A silicone rubber sheet 30 is provided between the actuator 2 and the base block 42. The holding plate 41 and the base block 42 press the nozzle plate 4 against the actuator 2 when a screw 43 is tightened.
The jig 50 is then mounted in a heating device such as an oven (not shown). The jig 50 is heated at about 150.degree. C. for 30 minutes. Accordingly, while being applied with pressure, the nozzle plate 4 and the actuator 2 are heated at about 150.degree. C. for 30 minutes. As a result, the epoxy resin is thermally hardened, thereby firmly attaching the nozzle plate 4 to the actuator 2.
It is noted that thus applying heat leads thermal expansion of the nozzle plate 4 and the actuator 2. However, the thermal expansion coefficient of the nozzle plate 4 is different from that of the actuator 2. This is because the nozzle plate 4 is generally made of polyimide resin, while the actuator 2 is made of piezoelectric ceramic. Therefore, after the heating process, the positions of the nozzles on the nozzle plate 4 are shifted from the positions of the ink channels in the actuator 2. The nozzles fail to be positioned precisely corresponding to the ink channels. Accordingly, when the thus produced assembly of the nozzle plate 4 and the actuator 2 is employed in a print head, the assembly attains poor ink ejection, and therefore degrades printing quality.
Additionally, during the heating process, the jig 50 is heated in the oven together with the nozzle plate 4 and the actuator 2. Because the nozzle plate 4, the actuator 2, and the jig 50 have large thermal capacities, the temperatures thereof increase gradually. As the temperatures of the actuator 2 and the nozzle plate 4 increase, the epoxy resin starts being hardened and discharging gas. However, when the temperature increases at a low rate, the gas is discharged slowly from the epoxy resin. As a result, when the epoxy resin is hardened completely, the gas is still remained in the epoxy resin. The gas thus trapped in the hardened epoxy resin forms air bubbles. If the air bubble is located on a surface of the hardened epoxy resin contacting the nozzle plate 4 or the actuator 2, a space is formed between the epoxy resin and the nozzle plate 4 or the actuator 2. Thus produced space weakens attachment between the nozzle plate 4 and the actuator 2. Also, when the nozzle plate 4 is wiped for maintenance during printing, the nozzle plate 4 will possibly drop from the actuator 2.